1. Field of the Invention
The present invention relates to a resin coating method and apparatus for applying resin to a predetermined region of a printed wiring board.
2. Description of Related Art
Conventionally, the production of semiconductor devices, in which semiconductor elements are mounted on a printed wiring board, involves the insertion of an insulating resin between the printed wiring board pad and the semiconductor bump and, further, the use of insulating resin in regions of the printed wiring board that include leads. This so-called underfill is intended to protect the circuit surface and to strengthen the bond between the semiconductor and the printed wiring board.
Generally, there are two main methods of applying the insulating resin (hereinafter simply resin): Injecting the resin between the printed wiring board and the semiconductor elements after the semiconductor elements have been mounted on the printed wiring board, and mounting the semiconductor elements on a printed wiring board that has already been coated with resin.
Of the two methods of application, the latter is further divided into exposure and stamp methods.
The exposure method involves spraying drops of resin from a nozzle that is moved over the surface of the printed wiring board, covering a predetermined region with a coating having a thickness, for example, of approximately 50-100 xcexcm.
By contrast, the stamp method involves dropping a predetermined amount of resin from a nozzle onto a central portion of the printed wiring board and then using the force with which the semiconductor elements are mounted on the printed wiring board to spread the resin over a predetermined region with a coating having a thickness, for example, of approximately 10-100 xcexcm.
The stamp method of application has come to be used with less frequency for large semiconductor elements with surface dimensions on the order of millimeters, being optimally suited to smaller semiconductor elements having surface dimensions of 0.3 mm or less.
An example of the mounting of such smaller semiconductor elements on a printed wiring board is shown in FIG. 1, which shows a head slider assembly for a hard disk drive. In this case, a head IC chip 1 is mounted on a printed wiring board suspension 2.
In such a case, the resin application device is usually a dispenser (not shown in the diagram) having a syringe filled with resin, the dispenser being able to raise and lower the syringe.
In order to apply the resin, a nozzle on a lower part of the syringe is positioned at a predetermined height above a surface of the suspension 2 and a predetermined amount of resin 3 is extruded from the syringe by compressed air. The extruded resin 3 is substantially spherical in shape, and contacts and adheres to the suspension 2. When the syringe is lifted the resin 3 separates from the syringe and spreads across a predetermined position on the surface of the suspension 2. Thereafter a head IC chip 1 is positioned above and pressed onto the suspension, thus further spreading the resin 3 as well as adhering and fixedly mounting the head IC chip 1 onto the suspension 2.
More specifically, as can be seen in FIG. 1, a wiring pattern 4 may be formed on a top surface of the suspension 2 and a gold pad 5 may be formed at an edge portion of the wiring pattern 5. At the same time, a gold bump 6 may be formed on a bottom surface of the head IC chip 1. The gold pad 5 and the gold bump 6 are coupled and a predetermined region between the head IC chip 1 and the suspension 2 including the gold pad 5 and the gold bump 6 is covered with the resin 3.
A plurality of suspensions 2 may for example be set atop a stage at a resin application device and the suspensions 2 subjected to the above-described coating process. In this case, in order to resin-coat a predetermined product lot with a predetermined amount of resin, the resin application device is set to specific conditions at the start of coating. When after repeated coating the resin is used up, a new syringe is installed.
In the above-described case, the head IC chip 1 is, for example, just 1xc3x971 mm, and so the amount of resin used in the coating is, for example, approximately 0.05 mg. Such small amounts over such small surfaces requires precision in the application of the resin 3.
However, because the amount of resin 3 involved in individual applications is small, it can happen that slight changes in ambient conditions during application, such as, for example, slight changes in temperature, causes slight changes in the amount of resin 3 applied, despite the resin application device being set to predetermined conditions beforehand.
Conventionally, in order to maintain the amount of resin 3 to be applied at the predetermined volume, a visual inspection is made of the amount of resin, if any, protruding from the edges of the semiconductor elements in a state in which the printed wiring board has been coated and the semiconductor elements mounted thereon in order to determine if too much resin or too little resin is being applied, after which the resin amount is adjusted as necessary. Additionally, visual inspection of the resin drop just before it separates from the nozzle or the external appearance of the resin 3 coating the stage are also used to determine the presence of change in the amount of resin applied.
However, the very small amounts of resin involved make it difficult to discern changes in that amount by the conventional methods. In addition, adjustment of the amount is often left to the discretion of an operator, which means it is often done manually and at arbitrary times. Such methods of adjustment are unsuited to cases in which the amount of resin applied changes continuously due to a variety of environmental and other factors.
Accordingly, it is an object of the present invention to provide an improved and useful resin coating method and apparatus in which the above-described disadvantage is eliminated.
The above-described object of the present invention is achieved by a resin coating method for applying resin to a predetermined region of a printed wiring board comprising the steps of:
imaging an external appearance of the resin extruded from a resin application device; and
automatically adjusting an amount of the resin extruded from the resin application device based on the external appearance of the resin obtained in the imaging step.
The above-described object of the present invention is also achieved by a resin coating apparatus for applying resin to a predetermined region of a printed wiring board, comprising:
an imaging unit for imaging an external appearance of the resin extruded from the resin coating apparatus; and
an automatic adjustment unit for automatically adjusting an amount of the resin extruded from the resin coating apparatus based on the external appearance of the resin obtained in the imaging step.
According to the above-described aspects of the present invention, the amount of resin expelled, in other words, the amount of resin to be used to coat the printed wiring board, is set according to the dimensions of the semiconductor elements mounted on the printed wiring board. The present invention is most effective with semiconductor elements measuring not more than 0.3 mm a side, though it is not limited to use with semiconductor elements of such dimensions.
A preferred method for automatically adjusting the amount of resin extruded from the resin coating apparatus is one in which a difference between a preset coating amount and an actual coating amount as determined by the external appearance of the resin is sensed and this difference used as feedback to adjust the amount of resin extruded. In this case, it is preferable that relational data relating the external appearance of the resin and the coating amount be stored as a reference table in the resin coating apparatus. An ordinary camera can suffice for use as the imaging device. As a method of adjusting the amount of resin extruded, it is preferable to regulate either the pressure of compressed air used to expel the resin, and/or the amount of time during which that flow of air continues. For accuracy and ease of control, regulating the timing of the air flow is preferable.
It should be noted that the foregoing can be applied to any or all of the embodiments to be described later.
It will be appreciated by those of skill in the art that the factors that directly affect the amount of resin extruded from the syringe and cause it to vary from a predetermined desired amount include but are not limited to changes in air pressure, changes in temperature, and changes in the viscosity of the resin due to changes in the components of the resin over time.
However, according to the above-described aspects of the present invention, the amount of resin extruded can be quickly and accurately adjusted as necessary.
Additionally, the above-described object of the present invention is also achieved by a resin coating method for applying resin to a predetermined region of a printed wiring board, comprising the steps of:
measuring a temperature of an extrusion nozzle of a resin application device; and
automatically adjusting an amount of the resin extruded from the resin application device based on the temperature of the nozzle.
According to this aspect of the invention, an appropriate temperature sensor can be used to measure the temperature of the extrusion nozzle, and the method of adjustment may be either manual or automatic.
Additionally, adjustments in the amount of resin extruded necessitated by changes in the amount of resin extruded from the extrusion nozzle due to a change in the viscosity of the resin caused by a change in the temperature of the nozzle can be performed relatively easily, on the basis of the temperature data. Additionally, if in this case the amount of resin extruded is adjusted automatically, then the amount of resin extruded can be quickly and accurately adjusted as necessary.
Additionally, the above-described object of the present invention is also achieved by a resin coating method for applying a resin to a predetermined region of a printed wiring board comprising positioning an extrusion nozzle of a resin application device at a predetermined reference height.
The reference height is not particularly limited. However, in terms of eliminating with certainty those elements that cause the amount of resin extruded to vary, controlling the height of the nozzle with respect to the printed wiring board on which the resin coating is to be applied is desirable. In this case, for example, a glass plate may be placed at a height identical to a height at which the printed wiring board is positioned, with an upper surface of the glass plate serving as a reference surface. The extrusion nozzle from which resin is extruded may then be contacted against the reference surface so as to adjust the nozzle to a reference height. The contact may be detected by a variety of suitable methods, including use of a magnetorestrictor to detect the presence of an electric current when pressure is applied or by using a light-emitting element and a light-receiving element to detect when the light is cut off. By programming the resin application device to raise and lower the syringe (or resin extrusion nozzle, as the case may be) according to a set schedule, the reference height contained in that program can be replaced with a newly obtained reference height.
According to the above-described aspect of the invention, the extrusion nozzle is positioned at a predetermined height when mounted on the resin application device, so the distance between the extrusion nozzle and the printed wiring board does not change even when, for example, the syringe containing the resin becomes empty and is replaced with a new syringe in an operation that can cause the height at which the extrusion nozzle is positioned to vary.
As a result, in the present invention the distance between the nozzle and the printed wiring board is set to a predetermined value and hence the volume of resin extruded does not change, hence avoiding a situation in which the height of the nozzle changes, and accordingly, the distance between the tip of the nozzle and the printed wiring board changes, such that when that distance exceeds a predetermined value the amount of resin extruded also exceeds a predetermined amount, and conversely, when that distance falls below a predetermined value the amount of resin extruded also decreases below a predetermined amount.
The above-described object of the present invention is also achieved by a resin coating method for applying resin to a predetermined region of a printed wiring board, comprising the steps of:
imaging an external appearance of a resin drop after the resin drop has been extruded from a nozzle of a resin application device but before the resin drop contacts the printed wiring board; and
adjusting a distance between a tip of the nozzle and the printed wiring board based on the external appearance of the resin drop obtained in the imaging step.
If for some reason the distance between the nozzle and the printed wiring board becomes too short, then when the nozzle is lifted after coating the printed wiring board resin remains on the tip of the nozzle. If such a condition persists, then at some point during the coating process the amount of residual resin remaining on the tip of the nozzle peels off therefrom, coating the printed wiring board with an abnormally large amount of resin.
However, according to the above-described aspect of the present invention, adhesion of excess resin to the tip of the nozzle can be prevented by, for example, substantially matching the distance between the tip of the nozzle and the printed wiring board to a diameter of the drops of resin. In this case, it would be even more desirable to compile a database relating resin drop diameter to optimal distance between the nozzle and the printed wiring board so as to automatically adjust the distance to the diameter.
Additionally, the above-described object of the present invention is also achieved by a resin coating method for applying resin to a predetermined region of a printed wiring board, comprising the steps of:
imaging a residual amount of the resin on an extrusion nozzle of a resin application device from which the resin is expelled; and
washing the nozzle when the residual amount exceeds a predetermined amount.
According to this aspect of the invention, by washing the nozzle before the coating amount varies from a desired amount, imperfections in the coating can be avoided.
In this case, any of a variety of suitable methods for washing the nozzle can be employed, including removing the residual resin by air blower, by wiper, by immersion in a washing solution or by melting the residual resin off.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.